1. Field of the Invention
This invention relates to a pearlescent concentrate with newtonian flow behavior in the form of a low-viscosity aqueous dispersion containing 10 to 40% by weight of pearlescing components.
Aqueous preparations of surfactants and cosmetic formulations can be given a pearlescent, aesthetically pleasing appearance by incorporation of substances which, after cooling, precipitate in the form of fine pearlescent crystals and remain dispersed in the preparations. Suitable pearlescing agents are, for example, the mono-, di- and optionally triesters of ethylene glycol or glycerol with C.sub.14-22 fatty acids, oligomeric alkylene glycol esters of this type, for example PEG-3-distearates, fatty acids and monoalkanolamides of fatty acids.
It is also known that the pearlescing agents mentioned can be stably dispersed in water or in aqueous emulsifier solutions and that the concentrated pearlescing dispersions obtained in this way can be added without heating to the preparations to be given a pearlescent appearance so that there is no need for the heating and cooling otherwise necessary for incorporation to form the pearlescent crystals.
One of the problems involved in the production and use of pearlescent concentrates concerns their flowability and pumpability. Both are often seriously limited, above all where the pearlescing components and emulsifiers are present in high concentrations. Alternatively, the concentrates may even assume the form of mixtures which do not flow and also cannot be pumped by conventional equipment.
2. Discussion of Related Art
Accordingly, it was proposed in German patent applications DE 38 43 572 and DE 41 03 551 to reduce the viscosity of pearlescent concentrates by addition of low molecular weight polyhydric alcohols and thus to make them flowable and pumpable.
International patent application WO 94/24248 discloses pearlescing agents based on alkyl polyglycoside/betaine surfactants which also contain glycols.
Although pearlescent concentrates sufficiently pumpable and flowable for conventional processing can be obtained in accordance with the teachings of these documents, these products are still not entirely satisfactory. The reason for this lies in the pronounced non-Newtonian or thixotropic behavior of the concentrates.
Thus, a thixotropic increase in viscosity is observed, in particular after prolonged storage. In addition, the yield point means that a more or less thick layer of product always remains behind on the walls of the storage container and can only be removed with immense effort or in the course of cleaning operations. In the latter case, therefore, part of the product is lost, i.e. is not available for processing. Finally, the pressure loss involved in the pumping of non-newtonian liquids is distinctly higher than for newtonian liquids which means that the pumping equipment has to meet increased performance requirements, particularly at the beginning of pumping.
Accordingly, there is still a need for pearlescent concentrates which are distinguished both by low viscosities, i.e. pumpability or flowability, and in particular by newtonian viscosity behavior.